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Action of  -Aminolevulinic
Acid and -Aminolevulinic
Acid Methyl Ester on Human Cancer Cells
Yow, Christine1
and Choi, Mabel1
The Hong Kong Polytechnic University1
Abstract-
Introduction: Nasopharyngeal Carcinoma (NPC) is squamous cell carcinomas
of the head and neck which is common in South China region. The annual
incidence rate in Hong Kong for male is 25.7 and for female is 11.2
per 100,000. In this study, -aminolevulinic
acid (ALA) and one of its derivatives, -aminolevulinic
acid methyl ester (ALA-methyl ester) were explored for their phototoxicity,
genotoxicity, cellular drug uptake and the intracellular localization
using NPC cells (NPC/HK1) as model. Materials and Methods: NPC/HK1 cells
were sensitized with various concentration of ALA and ALA-methyl ester
for 4 hrs followed by light dose. The phototoxicity of NPC/HK1 cells
was measured by Trypan Blue exclusion assay. Possible DNA damage induced
by both sensitizers were investigated using comet assay with the cell
viability greater than 50%. Drug uptake was quantitated by Flowcytometer
for both sensitizers using the Coulter Elite. Intracellular drug localization
was examined by Fluorescent microscopy. Results & Conclusions: Trypan
Blue exclusion assay showed that photodynamic dose of 0.5 mM ALA at
60 kJ/m2 resulted in 99.3% phototoxicity whereas 1.0 mM ALA
methyl ester at 60 kJ/m2 was required to achieve similar
cytotoxic effect. Hence, ALA is more efficient in killing NPC/HK1 cells.
No dark cytotoxicity was detected for either sensitizers. The level
of DNA damage was investigated with the LD50 photodynamic
dose by comet assay. No DNA damage was detected with cells treated with
both sensitizers immediately and 20 hours after treatment. By flowcytometry,
the protoporphyrin (PpIX) production differed between two sensitizers.
The drug uptake was greater in ALA. Notwithstanding, their localization
seems to be similar with plasma membrane and the cytoplasm as the target
sites. No nucleus staining was observed which may account for the absence
of DNA damage. ALA-based PDT demonstrated promising result in this cell
line.
Keywords: NPC,
PDT
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